If you have enough information about my DNA, my society, where I am now and what I'm doing, I think you'd be surprised how predictable each and every decision and action I make becomes.
ChatGPT 4, limited as it is, could probably predict me down to a low margin of error with that kind of info alone, and it would seem like magic to me.
A character on the NBC/Yahoo! show Community had a good one-liner: "I'm not psychic, Annie. That's just an illusion caused by extreme preparedness."
I think it would vary a lot depending on the specific decisions and how unique the combination of circumstances are. Even though things tend to repeat on a large enough scale, different combinations can still be highly unique.
OTOH when they are not... a simple exercise one can do is go ask GPT-4 to simulate a comment section on some political news story posted online; you can even have it write a fictional news story first, for good measure. It is extremely good at it, and that tells me volumes about the actual (rather than perceived) rationality of our public discourse.
There is a case that everything we do is preordained. A result of forces and interactions that trace all the way back to big bang.
My choice on whether or not I reply to you doesn't exist. Your combination of words triggers a response in my brain that makes me type this combination of words. The words I "chose" to delete, rewrite, leave, are all a result of various forces.
The kicker is that we can't really know. There is no test for free will. In order to know whether or not I had a choice to do this, we'd have to run the entire universe again up to that point to see what I would do. Because experience matters. Even if this exact same post went up tomorrow with all the same response except for mine. The fact that it's now Thursday instead of Wednesday matters. The fact that I posted this today matters. What I had for lunch. How fast I drank my coffee. What shirt I wore. Etc. These are all things that change the conditions under which I will engage with the post.
The second kicker is that it doesn't matter. If free will truly does not exist, it's not like you have a choice in whether or not to believe in it. The arguments either will work or they won't.
I don't understand how anyone can doubt this even a fraction of a second. Magic does not exist.